Eight Common Mesozoic Conifer Foliage Morphologies
Carboniferous – Recent
For artists required to reconstruct the life appearance of prehistoric trees and foliage, it is often useful to be able to contrast extinct foliage morphologies with living examples of a similar type.
Here I present a series of illustrations based on information presented by Stewart & Rothwell in their 1993 publication, Palaeobotany and the Evolution of Plants, contrasting some common Mesozoic conifer leaf types alongside their extant morphologically similar counterparts. The fossil species are the lighter of the paired illustrations.
It must be noted that these external morphological similarities do not suggest close genetic affinities but merely serve to suggest a possible life appearance for the purposes of illustration.
The genetic affinities between living and extinct conifers are hard to understand, with many extant species bearing superficial similarities to extinct genera. Recent taxonomic studies have reclassified the position of the conifer families, recognising the Taxaceae as a distinct monophyletic group within the Pinales, rather than a separate order.
For the purpose of illustrating prehistoric plants however, where we are concerned with appearances on the macroscopic rather than the microscopic level, it is useful to be able to observe and compare similarities between extinct and extant foliage morphotypes, with many prehistoric genera possessing fronds and leaves resembling living plants today.
Both Brachyphyllum and Pagiophyllum are recognised as belonging within the Araucariaceae. Brachyphyllum has small helically arranged pyramidal leaves with a broad basal cushion, resembling closely the shoots of Athrotaxis cupressoides.
Pagiophyllum leaves are wider and longer than the width of their basal cushion. Leaves of this kind are observed in Araucaria bidwillii.
Both genera form an overlapping boundary with the morphological characteristics of the fossil taxon Cyparissidium, the latter having narrow spirally arranged leaves held adjacent to the leaf axis. Glyptostrobus pensilis, the Chinese swamp cypress is a living example of a conifer with leaves of this kind, as are Taxodium ascendens and the podocarp Dacrydium cupressinum.
Another notable foliage morphotype recognised from the Permian period onwards, is Elatocladus. Elatocladus leaves can be arranged helically or opposite on the leaf stem with elongated dorsally flattened leaves narrowing where they adjoin the basal cushion. Examples of extant Elatocladus type foliage are Cephalotaxus, Amentotaxus, Taxodium distichum and Metasequoia. Unlike the other conifer families, Pityocladus and its living morphological representatives the Pinaceae are better represented in the Cenozoic than the Mesozoic, having evolved from their ancestors in the Jurassic to become the largest family of extant conifers. Pityocladus leaves belong in an order distinct from the other conifer families and bear foliage with two or more long acicular leaves radiating from a fascicle sheath. Podozamites has a leaf morphology superficially resembling that of a cycad; its large multi-veined leaves are lanceolate in shape and radiate alternately or helically, tapering where they meet the stem. Agathis is a good representative of the Podozamites morphotype. The fossil taxon Geinitzia has leaves morphologically similar to those of Pagiophyllum, being helically arranged along the leaf axis. However, Gentizia leaves are thinner needle-like structures that do not taper where they join the stem. Geinitzia leaf types are represented in the Taxodiodeae by Cryptomeria and in the Araucariaceae by Araucaria heterophylla, both species having shoots of this type. Cupressinocladus is a non-committal term assigned to fossil conifer foliage with shoots similar in their morphological characteristics to some members of the extant Cupressaceae, possessing small scale-like or dorsally flattened leaves arranged in whorls or decussate pairs appressed or spreading from the leaf stem. Thuja and Thujopsis are examples of living conifers with shoots that agree with the Cupressinocladus morphotype. Although we are discussing here the morphological similarities between extinct fossil foliage and living plants, it must be noted that these similarities may be purely superficial, and future fossil discoveries and microscopic research may disprove anything but a distant association, but for now being able to make these comparisons offers the artist the opportunity to reconstruct the external appearance of these dominant Mesozoic gymnosperms with a reasonable degree of certainty. For further reading refer to Stewart W.N & Rothwell G.W 1993 Paleobotany and the Evolution of Plants 2nd Edition. Ink on paper.
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